1) Field
Embodiments of this invention relate to the field of semiconductor devices and more particularly to a non-planar gate all-around device and method of fabrication.
2) Description of Related Art
As integrated device manufacturers continue to shrink the feature sizes of transistor devices to achieve greater circuit density and higher performance, there is a need to enhance transistor drive currents while reducing short-channel effects such as parasitic capacitance and off-state leakage for next-generation devices. One way of increasing transistor drive currents is to use higher carrier mobility semiconductor materials to form the channel. Higher carrier mobility in the channel supports higher transistor drive currents. Carrier mobility is a measure of the velocity at which carriers flow in a semiconductor material under an external unit electric field. Process induced stress (sometimes referred to as stress) on the semiconductor body is another way of increasing drive currents. Inducing stress on the semiconductor body enhances carrier mobility, thereby increasing the drive currents in transistor devices.
Non-planar transistors, such as the tri-gate transistor, are a recent development in semiconductor processing for controlling short channel effects. With tri-gate transistors, the gate is adjacent to three sides of the channel region. Because the gate structure surrounds the fin on three surfaces, the transistor essentially has three gates controlling the current through the fin or channel region. These three gates allow for fuller depletion in the fin and result in less short-channel effects due to steeper sub-threshold current swing (SS) and smaller drain induced barrier lowering (DIBL). Unfortunately, the fourth side, the bottom part of the channel is far away from the gate electrode and thus is not under close gate control. As transistor dimensions are continually scaled down to sub 20-25 nm technology nodes, parasitic leakage paths between the source and drains become problematic for tri-gate transistors.